The invention relates to a personal washing bar that provides effective cleansing, and a refreshing experience while producing lower levels of visual dryness, retaining more moisture in the skin and maintaining a stronger protective barrier than ordinary soap. The composition comprises soap, polyalkalene glycol, fatty acid, and the salt of specific protic acids. The personal washing bar combines these benefits with excellent in-use sensory properties as well as good bar properties.
Consumers are increasingly interested in milder ways to cleanse their skin which results in less damage of the skin""s natural protective barrier and also leads to the retention of more moisture in their skin. Indeed toilet bars based on synthetic surfactant such as the Dove(copyright) Beauty Bar have gained in popularity. Also, milder synthetic based liquids compositions are a growing segment of the market, especially among consumers in the more developed markets around the world.
However, the in-use properties of synthetic based bars and liquids (syndet bars and liquids) are quite different from soap. Synthetic based formulations tend to rinse slowly from the skin, often leave a feeling of a slippery residue remaining on the skin and are perceived not to last as long as soap. For many consumers in warm tropical climates, washing with syndet bars, combo bars and syndet liquids is not perceived to provide the level of cleansing and refreshing in-use sensory experience provided by soap and is a less preferred method of cleansing the skin even though washing with soap is harsher. Furthermore, because of the intrinsic cost of raw materials, packaging (for liquids), and the relatively higher use-up rates, mild syndet and combo bars and liquids makes these products out of reach of most consumers in emerging and developing markets even if they could learn to live with the very different cleansing experience.
There has been a great deal of research and development devoted to making soap bars milder. A recent review is provided by Murahata et al. (Cleansing Bars for Face and Body: In Search of Mildness, in Surfactants in Cosmetics, Ed M. Rieger and L. Rhein, 1997 Marcel Dekker, New York). The approaches include incorporation of relatively high levels of cationic polymers, mild synthetic surfactants, and the inclusion of a relatively high level of glycerol ( greater than 10%). All of these approaches have their limitations in terms of cost, manufacturing feasibility and impact on sensory properties and cost. One commercially successful approach is a so called xe2x80x9ccombo barxe2x80x9d of soap and a synthetic surfactant (e.g., acyl isethionate) as used for example in U.S. Pat. No. 4,954,282 to Resch et al. (relating to Lever 2000(copyright) type product). Even here, the sensory properties, use-up rates and cost do not match those of soap. Thus, there is a very real need for a method of cleansing the skin that is perceived to provide the refreshing cleansing experience and economy of soap while maintaining better skin care especially in the reduction of barrier damage and the increase in the level of moisture retention relative to common soap.
The present invention provides a method of cleansing the skin which is perceived as effective in removing oil and dirt, is preferred by consumers who like the sensory properties of soap, and provides improved skin care. In this context xe2x80x9cimproved skin carexe2x80x9d is defined as causing less damage to the skin""s naturally protective barrier, retention of more moisture in the skin, and/or reducing visible dryness than the method of cleansing the skin with an ordinary soap bar.
The invention further provides a bar which provides these cleaning and preferred sensory attributes while causing less damage to the skin""s naturally protective barrier, inducing a lower level of visual dryness and while retaining more moisture in the skin than ordinary soap bars.
The invention further provides a bar which provides these desirable perceived cleaning, and preferred sensory properties, and delivery of improved skin barrier protection and moisturization, yet has a cost that is comparable with soap.
EP Patent No. 0,707,631 to Chambers et al. discloses a soap bar composition comprising:
(a) 44 to 86.5% by wt. fatty acid soap;
(b) 5 to 30% by wt. polyalkylene glycol;
(c) 2.5 to 20% by wt. C6 to C22 fatty acid; and
(d) 6 to 20% water.
wherein ratio of polyalkylene glycol to C6 to C22 fatty acid is 1:3 to 3:1 and polyalkylene glycol has MW below 100,000 Dalton. There is no teaching of the specifically defined protic acid salts of the invention; of the ratios of these salts to free fatty acid; or of the sensory (soap-like clean) and skin care benefits (as measured by defined tests) provided when meeting the defined criteria of the invention.
Applicants have filed a continuation-in-part application to the equivalent of the U.S. Chambers application which claims 0.1 to 50% electrolyte and provides enhanced processing benefits. Again there is no teaching of the defined protic acid salts; of the ratios of these salts to free fatty acid or of enhanced skin care benefits.
Applicants have filed an application to Van Gunst et al. disclosing:
(a) 50 to 80% by wt. soap;
(b) 4 to 35% by wt. free fatty acid;
(c) 1 to 10% by wt. selected organic salts; and
(d) about 10% water;
wherein the bar has no more than about 4% synthetic and is processed using standard extrusion equipment.
The reference fails to disclose the defined protic acid salts, the ratio of protic acid salts to free fatty acid or enhanced skincare benefits.
Similarly, U.S. Pat. No. 3,598,746 to Kaniecki discloses soap free fatty acid and polyalkylene glycol, but fails to recognize defined protic acid salts, ratio of salts to free fatty acid or sensory properties and skin care benefits as measured in the subject invention.
The subject invention provides bar comprising fatty acid soaps, free fatty acids, polyalkylene glycol and specifically defined protic acid salts. Using these protic acid salts and defined ratios of the protic acid salts to free fatty acids, applicants have unexpectedly been able to obtain enhanced skin care properties as measured by defined tests, while achieving good desirable bar properties (e.g., hardness, low grit) and desirable sensory properties (e.g., clean rinsing).
More specifically, the invention comprises:
(a) 25 to 85% by weight fatty acid soap;
(b) polyalkylene glycol having MW of 400 to 25,000, preferably 400 to 10,000;
(c) 1 to 35% by weight C8-C22, preferably C10-C20, more preferably C10-C18 free fatty acid (saturated and unsaturated, preferably at least saturated); and
(d) 0.1 to 5% by wt., preferably 0.5 to 3% by wt. of a salt of a protic acid having a pKa1 of less than 6, preferably less than 5.5;
wherein the amount of polyalkylene glycol present in the bar must be sufficient to improve skin condition in Controlled Application Wash Tests either by reducing the barrier damage as measured by transepidermal water loss, increasing skin hydration as measured by skin conductivity/capacitance, and/or by reducing visual dryness as measured by objective grading.
In addition, the molar equivalents ratio of free fatty acid to protic acid salt is preferably between 0.5:1 to 3:1, most preferably between 0.75:1 to 3:1 and the weight ratio of free fatty acid to the sum of weights of PAG plus protic acid salt, i.e., (wt. % FA)/(wt. % PAG+wt. % protic acid salt) , should be between 1:2 to 2:1.
The molar equivalent ratio is defined by the following equation:
Grams Free Fatty Acid/Molecular Weight Free Fatty Acid
(Grams protic acid/Molecular Weight Protic acid)xc3x97(Number Equivalents per Mole Protic Acid)
The term equivalents is used in the ordinary chemical sense for protic acids and is equal to the number of moles of hydronium ions required to form the fully protonated conjugate acid of the protic acid salt.